Methods for testing multibeam satellite systems using input power telemetry and output noise power

ABSTRACT

Methods that test multibeam satellite communication systems, including its antennas and transponders. The methods use input power telemetry and output noise power to test satellite transponders and antennas while the satellite is in orbit. One method that tests a satellite receive antenna employs at least two earth stations, one for RF testing and one for telemetry and commanding, with each providing a backup for the other. Other methods may use one or more earth stations to perform testing. Methods are disclosed that generate receive antenna pattern measurements, transmit pattern measurements, input chain frequency response curves, input chain transfer curves, and output chain frequency response curves.

BACKGROUND

The present invention relates generally to satellite communicationsystems, and more specifically, to methods for testing multibeamsatellite communication systems in orbit using input power telemetry andoutput noise power.

The assignee of the present invention manufactures and deployssatellites carrying communication systems into geosynchronous and lowearth orbits. Certain coverage patterns provided by communicationsystems produce many small spot beams. In many cases, the receivepattern and the transmit pattern are not over the same geographicallocation on the earth. Therefore, many payload test earth stations arerequired for payload testing while the satellite is in orbit.

In general, in-orbit testing of a satellite includes verifying thehealth of transponders and verifying the pointing and shape of theantenna patterns. Typically, these tests are end-to-end and require anearth station to provide an uplink and an earth station to receive andanalyze the downlink signal. If the satellite's transmit and receiveantenna patterns do not cover the same geographical location, two ormore earth stations are required.

For satellites whose receive and transmit footprints cover essentiallythe same geographical area, (or if there are two earth stations, one inthe receive and one in the transmit pattern), the antenna patternverification is conducted by performing RF measurements whilemaneuvering the satellite through a set of attitude maneuvers. Saturatedflux density (SFD) and Effective Isotropic Radiated Power (EIRP) atsaturation are recorded along with satellite attitude telemetry, thenanalyzed, to determine the receive pattern and the transmit pattern.This method requires an uplink from an earth station and downlinkreception at an earth station. This method is used throughout theindustry.

For satellites whose receive and transmit footprints cover essentiallythe same geographical area (or if there are two earth stations, one inthe receive and one in the transmit pattern), the health of thetransponders is verified by executing transponder tests such asSFD/EIRP, power input versus power output, frequency response, etc.These test also require an uplink from an earth station and downlinkreception at an earth station. This method is used throughout theindustry.

For satellites that do not have an earth station in both the receive andtransmit patterns, there are two known methods that achieve receiveantenna pattern measurements in-orbit. One of these methods is used tomeasure receive antenna patterns of NSTARa and NSTARb satellitesdeployed by the assignee of the present invention, and the other is amethod disclosed in U.S. Pat. No. 6,157,817. There is currently nomethod to achieve transmit antenna patterns for satellites unless bothreceive and transmit footprints are covered by earth stations. There isalso no currently-available method to evaluate transponder health unlessboth receive and transmit footprints are covered by earth stations.

The NSTAR antenna pattern measurement method verifies a receive antennapattern by recording signal strength telemetry resulting from an RFuplink at discrete attitude positions. The satellite attitude iscommanded to a specified attitude position, an RF uplink test carrier isapplied, the signal strength telemetry from an on board power sensingdevice is recorded, the uplink is removed, then the satellite attitudeis commanded to the next attitude position. These steps are repeateduntil sufficient data is taken to analyze the RF pattern. The earthstation that provides the RF test uplink is a geographically separateearth station from the earth station that provides command andtelemetry.

In method disclosed in U.S. Pat. No. 6,157,817, the same earth stationprovides the RF test uplink and receives the telemetry. This presents arisk to the mission in the event the earth station becomes inoperable.

It would be desirable to have the capability of testing both thetransponders and antenna patterns of a satellite-based communicationsystems without the requirement of having an earth station in both thereceive and transmit footprints. This would allow for testing of theantenna patterns and transponders of multibeam satellites with a minimumnumber of earth stations. Accordingly, it is an objective of the presentinvention to provide for improved methods of testing multibeam satellitecommunication systems with a minimum of earth stations using input powertelemetry and output noise power.

SUMMARY OF THE INVENTION

To accomplish the above and other objectives, the present inventionprovides for methods for testing multibeam satellite communicationsystems, including antennas and transponders. The methods use inputpower telemetry and output noise power to test satellite transpondersand antennas while the satellite is in orbit. One of the methods employsat least two earth stations, one for RF testing and one for telemetryand commanding, with the RF test earth station providing a backup forthe telemetry and commanding earth station. The other methods may useone or more earth stations to perform testing.

A first exemplary method that generates receive antenna patternmeasurements comprises the following steps. The satellite attitude ispositioned so the starting orientation angle of the slew for the uplinkbeam under test is over the payload test earth station providing the RFtest uplink. Typically, the edge of the uplink beam pattern is chosen asthe start point for the subsequent slew. A test signal is uplinked fromthe earth station to a receive antenna on the satellite. Commands areuplinked from a second earth station that cause the satellite to performa slow constant attitude translation (slewing) over predeterminedorientation angles. The power level of the uplink test signal is sensedwhile the satellite is slewed. Downlink telemetry corresponding to thesensed power level and orientation angles are generated and transmittedto a second ground station that is located at a geographically distinctlocation from the first earth station. The sensed power level andorientation angles contained in the downlinked telemetry are processedand analyzed to verify the operation of the receive antenna.

The first exemplary method uses more than one earth station to performreceive antenna pattern measurements, compared to the use of a singleearth station disclosed in U.S. Pat. No. 6,157,817. The improvementprovided by the present invention over the NSTAR method is that, insteadof commanding discrete attitude steps to perform receive antenna patternmeasurements, the present method commands a slow, continuous, constantattitude sweep. This allows for more data points to be taken, andreduces the time for the sweep. Slewing of the satellite is faster thanthe stop and measure technique used to test NSTAR satellites.

A second exemplary method uses a single earth station to generatetransmit antenna pattern measurements without using an uplink carrier.The second exemplary method comprises the following steps. The satelliteattitude is positioned so the start orientation angle of the slew forthe downlink beam under test is over the payload test earth stationreceiving the downlink noise. Typically, the edge of the downlink beampattern is chosen as the start point for the subsequent slew. Commandsare uplinked from an earth station that causes the satellite to performa slow constant attitude translation over predetermined orientationangles. Downlink noise power of a transponder is received at the earthstation and measured in a specified bandwidth while the satellite isslewed. Downlink telemetry corresponding to the orientation angles aregenerated and transmitted to the earth station. The measured noise powerlevels and orientation angles contained in the downlink telemetry areprocessed and analyzed to verify the operation of the transmit antenna.

A third exemplary method generates an input chain frequency responsecurve that serves to verify the frequency characteristics of thetransponder equipment up to the signal strength telemetry monitoringcircuit. This method comprises the following steps. The uplink beamcorresponding to the transponder equipment under test is positioned overa payload test earth station. RF signals at selected frequencies havingthe same power level are uplinked from the earth station to thesatellite. Downlink telemetry corresponding to the signal strength isgenerated and transmitted to the earth station. The signal strengthtelemetry, earth station uplink power and frequency are recorded andprocessed produce the input chain frequency response curve.

A fourth exemplary method generates an input chain transfer curve thatserves to verify the power characteristics of the transponder equipmentup to the signal strength telemetry monitoring circuit. This methodcomprises the following steps. The uplink beam corresponding to thetransponder equipment under test is positioned over a payload test earthstation. RF signals at selected power levels having the same frequencyare uplinked from the earth station to the satellite. Downlink telemetrycorresponding to the signal strength is generated and transmitted to thepayload test earth station. The signal strength telemetry and earthstation uplink power is recorded and processed to produce the inputchain transfer curve.

A fifth exemplary method that generates an output chain frequencyresponse curve that serves to verify the frequency characteristics ofthe entire transponder if the transponder is in a linear gain mode orfrom the output of an amplifier (TWTA) to the downlink antenna if thetransponder is in automatic level control mode. This method comprisesthe following steps. A downlink beam is positioned over an earthstation. The noise power within a small bandwidth centered around aselected one of a plurality of frequencies of interest is measured at anearth station. The noise power measurements are continued until thenoise power at all frequencies of interest are measured. The recordednoise power measurements are processed to generate an output chainfrequency response curve.

A sixth exemplary method that verifies the gain of the transpondercomprises the following steps. A downlink beam is positioned over anearth station. The noise power over a small bandwidth at centerfrequency or other frequency of interest is measured at an earthstation. The noise power measurements are made in both linear mode andautomatic level control mode at a variety of gain/level steps, if thesatellite is equipped with commandable gain/level steps. The recordednoise power measurements are processed to generate gain characteristicsof the transponder.

BRIEF DESCRIPTION OF THE DRAWINGS

The various features and advantages of the present invention may be morereadily understood with reference to the following detailed descriptiontaken in conjunction with the accompanying drawing, wherein likereference numerals designate like structural elements, and in which:

FIG. 1 illustrates an exemplary system in which methods in accordancewith the principles of the present invention are employed; and

FIGS. 2-7 are flow diagrams that illustrate exemplary methods inaccordance with the principles of the present invention for use with thesystem shown in FIG. 1.

DETAILED DESCRIPTION

Referring to the drawing figures, FIG. 1 illustrates an exemplary system9 in which the present methods 20, 30, 40, 50, 60, 70 are employed. Thesystem 9 comprises a satellite 10, payload test earth stations 18, andtelemetry and command earth station 19. The satellite 10 comprisestransponders 11, receive antennas 12, and transmit antennas 13 that areto be tested. The payload test earth stations 18 and telemetry andcommand earth station 19 are at geographically separate and distinctlocations. The exemplary system 9 is used in conjunction with variousmethods 20, 30, 40, 50, 60, 70 in accordance with the principles of thepresent invention to provide for testing of the transponders 11 andantennas 12, 13.

The present systems 9 and methods 20, 30, 40, 50, 60, 70 provide for animprovements over the technique used with regard to NSTARa and NSTARbsatellites deployed by the assignee of the present invention. Thepresent systems 9 and methods 20, 30, 40, 50, 60, 70 also provideimprovements over the teachings of U.S. Pat. No. 6,157,817. The contentsof U.S. Pat. No. 6,157,817 are incorporated herein by reference in itsentirety.

FIG. 2 is a flow diagram that illustrates a first exemplary procedure ormethod 20 in accordance with the present invention that is employed inconjunction with the system 9 shown in FIG. 1. The method 20 generatesreceive antenna pattern measurements that verify operation of thereceive antenna 12 on the satellite 10. The steps of the exemplaryreceive antenna pattern measurement method 20 are as follows.

A receive antenna pattern is positioned 21 over a payload test earthstation 18. This position is the start point for the subsequent slew andtypically is the edge of the pattern. An RF test signal is uplinked 22from a payload test earth station 18, to a receive antenna 12 on thesatellite 10.

Commands 16 are uplinked 23 to the satellite 10 from a telemetry andcommand earth station 19 that cause a slow constant attitude translation(slewing) over predetermined orientation angles. The power level of theuplink test signal is sensed 24 in a transponder 11 on-board thesatellite 10 while the satellite is slewed. Downlink telemetry 17corresponding to the sensed power level and orientation angles isgenerated 25 on-board the satellite 10 and downlinked.

The downlink telemetry 17 is received 26 at a telemetry and commandearth station 19 that is located at a geographically separate locationfrom the payload test earth station 18. The sensed power level andorientation angles contained in the downlinked telemetry 17 are recordedand processed 27 to verify the operation of the receive antenna 12 onthe satellite 10.

FIG. 3 is a flow diagram that illustrates a second exemplary method 30that generates transmit antenna pattern measurements to verify operationof the transmit antenna 13. The purpose of the transmit antenna patternmeasurement method 30 is to allow one earth station 18 to accurately mapany of the transmit spot beams generated by the satellite 10 withoutusing multiple payload test earth stations.

The second method 30 requires no uplink carrier, but the satellitetransponder 11 must be able to generate enough noise to be received atthe payload test earth station 18. This may be achieved by placing thetransponder in automatic level control mode. An exemplary transmitantenna pattern measurement method 30 is as follows.

The gain of the transponder 11 is configured 31 to establish a suitablenoise pedestal at the payload test earth station 18. The transmitantenna 13 pattern is positioned 32 over the payload test earth station18. This position is the start point for the subsequent slew andtypically is the edge of the pattern.

Commands 16 are uplinked 33 to the satellite 10 from a telemetry andcommand earth station 19 that cause a slow constant attitude translation(slewing) or discrete steps in attitude over predetermined orientationangles. Downlink noise 15 of the transponder 11 is transmitted 34 to thepayload test earth station 18, where it is measured and recorded.

Downlink telemetry 17 corresponding to the orientation angles isgenerated 35 on-board the satellite 10 and transmitted 36 to a commandand telemetry earth station 19. The noise power measurements andsatellite attitude are recorded and processed 37 to verify the operationof the transmit antenna 13.

FIG. 4 is a flow diagram that illustrates a third exemplary method 40that generates an input chain frequency response curve. The objective ofthis method is to verify the health of the input chain using signalstrength telemetry. The input chain typically includes receive antennafeeds, input multiplexer, receiver, and channel amplifier. This methodwill verify all equipment up through the signal strength telemetrymonitoring point, which is typically, but not necessarily, in thechannel amplifier. The method 40 comprises the following steps.

An uplink beam 12 is positioned 41 over a payload test earth station 18and the attitude of the satellite 10 is held stationary. An RF testsignal at one of several selected frequencies of interest at a specifiedpower level is uplinked 42 from the payload test earth station 18 to thesatellite 10.

The signal strength of the uplink test signal is sensed 43 in thetransponder 11 on-board the satellite 10. Downlink telemetry 17corresponding to the signal strength is generated 44 on-board thesatellite 10 and downlinked.

The downlinked signal strength telemetry 17 is received 45 at atelemetry and command earth station 19. The signal strength telemetry 17and RF test carrier frequency is recorded 46.

The above steps (42-43) are repeated 47 until all frequencies ofinterest are uplinked and signal strength telemetry is recorded 46. Therecorded signal strength telemetry and RF test carrier frequency areprocessed 48 to produce the input chain frequency response curve.

FIG. 5 is a flow diagram that illustrates a fourth exemplary method 50that generates an input chain transfer curve. The objective of thismethod 50 is to verify the health of the input chain using signalstrength telemetry. The input chain typically includes receive antennafeeds, input multiplexer, receiver, and channel amplifier. This method50 verifies all equipment up through the signal strength telemetrymonitoring point, which is typically, but not necessarily, in thechannel amplifier. The method 50 comprises the following steps.

An uplink beam 12 is positioned 51 over an earth station 18 and theattitude of the satellite 10 is held stationary. An RF test signal atone of several power levels of interest at a specified frequency isuplinked 52 from the payload test earth station 18 to the satellite 10.

The signal strength of the uplink test signal is sensed 53 in thetransponder 11 on-board the satellite 10. Downlink telemetry 17corresponding to the signal strength is generated 54 on-board thesatellite 10 and downlinked.

The downlinked signal strength telemetry 17 is received 55 at atelemetry and command earth station 19. The signal strength telemetry 17and RF test carrier power level are recorded 56. This is repeated untilall power levels of interest are uplinked and signal strength isrecorded. The recorded signal strength telemetry and RF test carrierpower level are processed 57 to produce the input power transfer curve.

FIG. 6 is a flow diagram that illustrates a fifth exemplary method 60that generates an output chain frequency response curve. The objectiveof this method is to verify the health of the output chain usingdownlink noise power. No uplink is required. The output chain includestypically includes high power amplifier (traveling wave tube (TWT) orsolid state power amplifier (SSPA), filter, output multiplexer, transmitantenna feeds. The method 60 comprises the following steps.

A downlink beam 13 is positioned 61 over an earth station 18 and theattitude of the satellite 10 is held stationary. The downlink noisepower 15 within a small bandwidth centered around a selected frequencyof interest is measured 62 at the earth station 18.

The noise power measurements are continued 63 until the noise power atall frequencies of interest are measured. The recorded noise powermeasurements are processed 64 at the earth station 18 to generate anoutput chain frequency response curve.

FIG. 7 is a flow diagram that illustrates a sixth exemplary method 70that generates a power level measurement of the transponder. Theobjective of this method is to verify the health of the output chainusing downlink noise power. No uplink is required. The output chainincludes typically includes high power amplifier (traveling wave tube(TWT) or solid state power amplifier (SSPA), filter, output multiplexer,transmit antenna feeds. The method 70 comprises the following steps.

A downlink beam 13 is positioned 71 over an earth station 18 and theattitude of the satellite 10 is held stationary. The downlink noisepower 15 within a small bandwidth at the center frequency is measured 72at the earth station 18. These steps are repeated 73 for a variety ofgain steps, if the satellite is equipped with commandable gain steps.

Thus, various methods for testing in-orbit multibeam satellitecommunication systems using input power telemetry and output noise powerbeen disclosed. It is to be understood that the above-describedembodiments are merely illustrative of some of the many specificembodiments that represent applications of the principles of the presentinvention. Clearly, numerous and other arrangements can be readilydevised by those skilled in the art without departing from the scope ofthe invention.

1. A method of testing a satellite transmit antenna of a multibeamsatellite system, comprising the steps of: uplinking commands from anearth station to a satellite to cause a translation of the satellite;transmitting downlink telemetry comprising orientation angles of thesatellite from the satellite to a telemetry and command earth station;measuring downlink noise in a small bandwidth at the telemetry andcommand earth station while the satellite is translated; and processingthe noise power level and orientation angles to verify operation of thetransmit antenna on the satellite.
 2. The method recited in claim 1wherein the uplinked commands cause a slow constant attitude translationof the satellite.
 3. The method recited in claim 1 wherein the uplinkedcommands cause a discrete steps in attitude translation of thesatellite.
 4. A method of generating an input chain frequency responsecurve for a multibeam satellite communication system, comprising thesteps of: positioning an uplink beam is over an earth station; uplinkingsignals at different frequencies of interest from the earth station tothe satellite; generating downlink telemetry on-board the satellite thatcorresponds to the signal strengths of respective signals at thedifferent frequencies; transmitting the signal strength telemetry fromthe satellite to the earth station; recording the signal strengthtelemetry and uplink frequency at the earth station; and processing therecorded signal strength telemetry and uplink frequency to produce theinput power frequency response curve.
 5. The method recited in claim 4wherein the signal strength telemetry is transmitted to a second earthstation that is located at a geographically separate location from theuplinking earth station.
 6. A method of generating an input chaintransfer curve for a multibeam satellite communication system,comprising the steps of: positioning an uplink beam is over an earthstation; uplinking RF signals at a plurality of power levels from theearth station to the satellite; generating downlink telemetry on-boardthe satellite that corresponds to the signal strengths of respectivesignals at the different power levels; transmitting the signal strengthtelemetry from the satellite to the earth station; recording the signalstrength telemetry at the earth station; and processing the recordedsignal strength telemetry to produce the input chain transfer curvecorresponding to input power frequency response.
 7. The method recitedin claim 6 wherein the signal strength telemetry is transmitted to asecond earth station that is located at a geographically separatelocation from the uplinking earth station.
 8. A method of generating anoutput chain frequency response curve for a multibeam satellitecommunication system, comprising the steps of: positioning a downlinkbeam is over an earth station; measuring noise power of the downlinkbeam over a small bandwidth centered around a plurality of selectedfrequencies of interest at the earth station; processing the noise powermeasurements to generate the output chain frequency response curve.
 9. Amethod of generating a gain measurement of a transponder of a multibeamsatellite communication system, comprising the steps of: positioning adownlink beam is over an earth station; measuring noise power of thedownlink beam over a small bandwidth at a selected frequency at theearth station; processing the recorded noise power measurements togenerate a gain measurement of the transponder.
 10. The method recitedin claim 9 wherein the noise power of the downlink beam is measured atthe center of the bandwidth at the selected frequency.